This invention relates to a protective device to indicate the possible entry of fluid including liquid substances into the interior of a drive motor for an underground mining machine especially drum-type coal mining machines. Drum or roller-type coal cutting machines consist, in the present state-of-the-art, of a large number of flange connected components. Such underground mining machines are equipped with one or two cutting drums and they include one or sometimes two drive motors, depending upon the desired capacity of the mining machine. A gear head or turret having a drive motor together with cutting drums and worm gears or screw jacks form a single unit which is rigidly attached together to form a compact part of the machine body. The arrangement of parts is such that the ends of the drive shaft project out of the opposite end faces of the drive motor into neighboring gear heads. The drive shaft actually extends into a reducing gear to drive the gear head at one end of the motor and into a worm gear drive at the other end of the motor.
During the extraction operation, the drum cutting machine must travel in a manner so as to follow the direction of a coal seam, for example. As a result, the position of the machine frequently changes from the horizontal and therefore the integrity of the seals must remain effective at those places where the ends of the drive shaft enter into the gear head and the worm gear, respectively. The integrity of these seals is important to the assurance that no lubricating oil from the reduction gearing will penetrate or otherwise find its way into the drive motor causing damage to the motor's winding should the extraction machine be tilted at an angle.